Back in 2004, the USGA made a change to the ODS test procedure, increasing the test speed to 120 mph and extending the ODS to 320 yards. They also changed the way the test was done as described below. Interesting that each mph was only going to add to 2.2 yards to the distance (11 mph for 24 yards). In the current proposed change it is going to be 15 yards for 5 mph. I guess there was little squawking then because they said all, then current, balls would still be conforming.
I expect that the current roll back will include other test procedure changes as well, including the launch conditions. IIRC correctly there was some talk of using the optimal launch conditions for each ball.
"Phase II updates the USGAs ball test procedures and the resulting Overall Distance Standard (ODS). The current ball test procedure and ODS standard were adopted in 1976 and have remained largely unchanged since that time. The changes to the test under Phase II are as follows:
Swing speed will be increased to 120 miles per hour from 109 miles per hour;
1. A non-branded titanium club head will replace the laminated wooden head now in use;
2. A modern, non-branded set-up ball will replace the current set-up ball that has been in use.
3. The ODS limit has increased from 296.8 to 320 yards
The ODS limit increase is due to the increased test swing speed and the switch to a modern titanium test club. It does not result in any additional golf ball distance allowance. All golf balls that currently appear on the USGAs List of Conforming Golf Balls will continue to comply with the Rules under Phase II conditions."
As for the cost of the changes to the manufacturers, I don't share Eric's cost concerns. Titleist in particular has quite a number of balls already with different performance characteristics (including lately the left dash and left dot Pro V1). They evidently do a lot of R&D to develop those balls with new ones coming out each year. I expect that all that will happen is that they will continue their R&D efforts with a slightly different distance target. They have a couple of years to get it right. I'd also imagine that over the years that they have tried many different combinations of designs and materials, some that have succeeded and some that have failed, that would give them insight into making multiple different shorter balls for different markets.
If making these small changes is so costly then I expect that many of the smaller ball manufacturers will go bankrupt or the cost of balls will go significantly up.